In the personal navigation field, navigation devices which utilize satellite signals for a position determination have gained acceptance in many areas of application, for example, as a carried-along global positioning system acquisition unit for hikers and climbers or for pedestrian tourists in a city. However, such navigation devices have the disadvantage that navigation functions perfectly only in the open air. Such navigation devices, which utilize satellite signals for a position determination, are not suitable for persons who are situated in buildings and can therefore not meet the demand for movement and position information in basements of large cities, in department stores, in museums, in airports and railway stations, as well as in basements of other companies or government buildings, for example. Currently, dedicated systems for interior applications—so-called indoor systems, for example, with infrared beacons—are used, which require high infrastructure expenditures.
It is an object of the invention to provide a method and a system for recognizing a pedestrian's step for a portable terminal, and to provide a portable terminal, which permit a reliable and cost-effective recognition of the pedestrian's step also in interior spaces.
This and other objects are achieved, according to a first and second aspect, by a method and a corresponding system for recognizing a pedestrian's step for a portable terminal, which has an acquisition unit. In an image of a sequence of images acquired by the acquisition unit, an object is in each case detected which represents at least a part of a foot, a shoe, and/or a leg. The position of the object is determined in the respective image, and a pedestrian's step is recognized as a function of a position change of the object between at least two images of the sequence of images.
An analysis of the respective image makes it possible to recognize the appearance and disappearance of the pedestrian's foot or of the tip of the pedestrian's foot and to use a step count and/or an estimation of the length of a step for recognizing a step. The determination of the steps can advantageously take place independently of further hardware components, particularly independently of further sensors, which are designed for acquiring measured data representative of a pedestrian's movement. This permits a cost-effective production of the terminal. The method according to the invention can be used for a step recognition for pedestrians moving in buildings as well as for pedestrians who are moving in the open air. The method according to the invention further has the advantage that steps can be reliably recognized even if the walking movement is slow and/or if the walking movement is irregular.
When acquiring the respective images, the terminal is preferably arranged on the pedestrian or is held by the pedestrian such that an image acquisition range of the acquisition unit, in each case, comprises a specified range in front of the pedestrian in the walking direction. The acquisition unit and/or a further appropriately designed unit of the terminal may be designed for signaling to the pedestrian by means of the output of signals, for example, visual signals, a specified positioning of the acquisition unit.
In an advantageous further development, the object is detected as a function of a similarity comparison of a specified model with the respective image. This permits a simple and reliable detection of the object.
In a further advantageous development, the model is determined as a function of an image detail of one of the acquired images, which includes at least a tip of the pedestrian's foot and/or shoe. This makes it possible to adapt the model to specific features of the pedestrians foot or shoe and therefore increase a reliability of the object detection and/or of the step recognition.
In a further advantageous development, a course of the position of the object is determined for the sequence of images, and the step is recognized as a function of the course. Advantageously, the respective step can thereby be very easily and reliably recognized.
In a further advantageous development, the image is subdivided into several image details, which may overlap. The similarity comparison with the model is carried out for each image detail. The position of the object is determined as a function of the image detail that has the greatest similarity to the model.
In a further advantageous development, the respective image has a matrix of pixels. For all central pixels, which each represent a center point of the respective image detail, one comparison value respectively is determined which represents a measurement for the similarity of the model to the respective image detail. The position of the object is determined as a function of the determined comparison values. This advantageously permits a simple detection of the object. The comparison value may, for example, represent a cross correlation coefficient, which is determined for the respective central pixel as a function of a cross correlation between the image detail and the model.
In a further advantageous development, a maximal comparison value is determined as a function of the comparison values, and the model is adapted when the maximal comparison value falls below a specified limit value. An analysis of the maximal comparison values permits the detection of changed conditions in the pedestrian's surroundings. This can be utilized for adapting the model to the changed conditions, for example, for adapting the model to changed brightness conditions.
In a further advantageous development, the pixels of the image have one color value respectively for a specified quantity of color channels. For at least one portion of the quantity of color channels, the comparison values are determined for the respective color channel. This advantageously allows a reliable similarity comparison of the image detail with the model and can thereby contribute to being able to very easily and reliably recognize the respective step. In this case, the respective color channel represents a primary color of a color space used for storing the image. A red-green-blue image (RGB image), for example, has three color channels, one each for red, green and blue. A CYMK image (cyan, yellow, magenta and black) has four color channels, one each for cyan, yellow, magenta and the black fraction.
In a further advantageous development, the pixels of the image each have a gray value from a specified quantity of gray values. Before the similarity comparison, an average gray value of the image is determined as a function of the gray values of at least a portion of the pixels, and the image is converted to a binary image, in which the respective pixels can assume only one of two conceivable gray values such that, as a function of the average gray value and the gray value of the respective pixel, the respective pixel has a specified first or second gray value. Advantageously, this permits a very simple and fast detection of the object. In the case of the binary image, the first gray value preferably represents the color white and the second gray value represents the color black. For determining the average gray value, for example, a gray-value histogram can be determined for the image, and the average gray value can be determined as a function of a variance of the gray values.
According to a third aspect, the invention is distinguished by a portable terminal which has an acquisition unit and a system according to the second aspect. Here, advantageous further developments of the first and second aspect also apply to the third aspect.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.